The study team was led by Adrian Martineau, Ph.D., from the Centre for Primary Care and Public Health at the Queen Mary University of London. The researchers reviewed data from 25 studies of vitamin D supplementation, representing 11,321 adults and children.

The investigators observed an association between taking vitamin D supplements and a decreased likelihood of having an acute respiratory infection. The 12 percent reduction meant that 33 people would need to take vitamin D supplements to prevent one acute respiratory tract infection. The benefit of the supplements was greater among people who took daily or weekly vitamin D without additional large doses. The protective effect of vitamin D supplements was strongest for those with severe vitamin D deficiency. In this group, four people would need to take vitamin D supplements to prevent one acute respiratory infection.

The results are inconclusive and need to be confirmed in carefully controlled clinical trials, said Mark Bolland, M.B.Ch.B., Ph.D., from the University of Auckland in New Zealand, and Alison Avenell, M.D., from the University of Aberdeen in the United Kingdom, the authors of an accompanying editorial in the journal. "Current evidence does not support the use of vitamin D supplementation to prevent disease, except for those at high risk of osteomalacia," they write.